(a) Field of the Invention
The present invention relates to a display device and a driving device of a light source thereof.
(b) Description of Related Art
An artificial light source, which is part of a backlight assembly, is often implemented as a plurality of fluorescent lamps such as CCFLs (cold cathode fluorescent lamps) and EEFLs (external electrode fluorescent lamps) driven by an inverter. The inverter converts a DC voltage into an AC voltage and applies the AC voltage to the lamps to be turned on. The inverter adjusts luminance of the lamps based on a luminance control signal to control the luminance of the LCD. In addition, inverter feedback controls the voltages applied to the lamps based on the currents of the lamps.
For controlling a plurality of CCFLs, the backlight assembly also includes a plurality of transformers connected to the lamps to apply a high voltage to a hot electrode of each CCFL, and a resistor sensing currents flowing through the CCFLs and connected between cold electrodes of the CCFLs and a ground. The sensed current is relative to the total current plus the current flowing through the cold electrode of each CCFL. Thus, the operating states of the CCFLs are not exactly determined in using the sensed current.
Display devices used for monitors of computers and television sets generally include self-emitting display devices such as organic light emitting displays (OLEDs), vacuum fluorescent displays (VFDs), field emission displays (FEDs), and plasma panel displays (PDPs), and non-emitting display devices such as liquid crystal displays (LCDs) requiring an external light source.
An LCD includes two panels provided with field-generating electrodes and a liquid crystal (LC) layer having dielectric anisotropy and interposed therebetween. The field-generating electrodes that are supplied with electric voltages generate electric field across the LC layer, and the light transmittance of the liquid crystal layer varies depending on the strength of the applied field, which can be controlled by the applied voltages. Accordingly, desired images are displayed by adjusting the applied voltages.
The light for an LCD is provided by lamps equipped at the LCD, or may be natural light.
The lamps for the LCD, which is a part of a backlight assembly, usually include fluorescent lamps such as CCFLs (cold cathode fluorescent lamps) and EEFLs (external electrode fluorescent lamps) driven by an inverter. The inverter converts a DC voltage into an AC voltage and applies the AC voltage to the lamps to be turned on. The inverter adjusts luminance of the lamps based on a luminance control signal to control the luminance of the LCD. In addition, the inverter feedback controls the voltages applied to the lamps based on the currents of the lamps.
Since, for driving the LCD, the backlight assembly is directly supplied with an external AC voltage, that is, a high common power source of a high current of about 110V or 220V, the dangers of electric shock to people and of lightning become large. Thus, to protect against these dangers, the backlight assembly must be supplied with a separate DC voltage of a high voltage and a low current separated from the common power source, which is transformed by a DC-DC converter. Due to the separate DC-DC converter, the manufacturing cost and consumption power are increased. In addition, the weight and size of the backlight assembly increase, thereby the design efficiency of the display devices is decreased.